'\" te
.\" Copyright (c) 2002, Sun Microsystems, Inc. All Rights Reserved
.\" Copyright 1989 AT&T
.\" The contents of this file are subject to the terms of the Common Development and Distribution License (the "License").  You may not use this file except in compliance with the License.
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.\" When distributing Covered Code, include this CDDL HEADER in each file and include the License file at usr/src/OPENSOLARIS.LICENSE.  If applicable, add the following below this CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your own identifying information: Portions Copyright [yyyy] [name of copyright owner]
.TH DRAND48 3C "June 20, 2021"
.SH NAME
drand48, erand48, lrand48, nrand48, mrand48, jrand48, srand48, seed48, lcong48
\- generate uniformly distributed pseudo-random numbers
.SH SYNOPSIS
.nf
#include <stdlib.h>

\fBdouble\fR \fBdrand48\fR(void)
.fi

.LP
.nf
\fBdouble\fR \fBerand48\fR(\fBunsigned short\fR \fIx\fR(i)[3]);
.fi

.LP
.nf
\fBlong\fR \fBlrand48\fR(void)
.fi

.LP
.nf
\fBlong\fR \fBnrand48\fR(\fBunsigned short\fR \fIx\fR(i)[3]);
.fi

.LP
.nf
\fBlong\fR \fBmrand48\fR(void)
.fi

.LP
.nf
\fBlong\fR \fBjrand48\fR(\fBunsigned short\fR \fIx\fR(i)[3]);
.fi

.LP
.nf
\fBvoid\fR \fBsrand48\fR(\fBlong\fR \fIseedval\fR);
.fi

.LP
.nf
\fBunsigned short *\fR\fBseed48\fR(\fBunsigned short\fR \fIseed16v\fR[3]);
.fi

.LP
.nf
\fBvoid\fR \fBlcong48\fR(\fBunsigned short\fR \fIparam\fR[7]);
.fi

.SH DESCRIPTION
This family of functions generates pseudo-random numbers using the well-known
linear congruential algorithm and 48-bit integer arithmetic.
.sp
.LP
Functions \fBdrand48()\fR and \fBerand48()\fR return non-negative
double-precision floating-point values uniformly distributed over the interval
[0.0, 1.0).
.sp
.LP
Functions \fBlrand48()\fR and \fBnrand48()\fR return non-negative long integers
uniformly distributed over the interval [0, 2^31].
.sp
.LP
Functions \fBmrand48()\fR and \fBjrand48()\fR return signed long integers
uniformly distributed over the interval [-2^31, 2^31].
.sp
.LP
Functions \fBsrand48()\fR, \fBseed48()\fR, and \fBlcong48()\fR are
initialization entry points, one of which should be invoked before either
\fBdrand48()\fR, \fBlrand48()\fR, or \fBmrand48()\fR is called. (Although it is
not recommended practice, constant default initializer values will be supplied
automatically if \fBdrand48()\fR, \fBlrand48()\fR, or \fBmrand48()\fR is called
without a prior call to an initialization entry point.) Functions
\fBerand48(\|),\fR \fBnrand48(\|),\fR and \fBjrand48()\fR do not require an
initialization entry point to be called first.
.sp
.LP
All the routines work by generating a sequence of 48-bit integer values, X(i ),
according to the linear congruential formula
.sp
.LP
X(n+1)= (aX (n)+c)(mod m) n>=0.
.sp
.LP
The parameter \fIm\fR = 2^48; hence 48-bit integer arithmetic is performed.
Unless \fBlcong48()\fR has been invoked, the multiplier value \fIa\fR and the
addend value \fIc\fR are given by
.br
.in +2
\fIa\fR = 5DEECE66D(16) = 273673163155(8)
.in -2
.br
.in +2
\fIc\fR = B(16) = 13(8)
.in -2
.sp
.LP
The value returned by any of the functions \fBdrand48()\fR, \fBerand48()\fR,
\fBlrand48()\fR, \fBnrand48()\fR, \fBmrand48()\fR, or \fBjrand48()\fR is
computed by first generating the next 48-bit X(i) in the sequence. Then the
appropriate number of bits, according to the type of data item to be returned,
are copied from the high-order (leftmost) bits of X(i) and transformed into the
returned value.
.sp
.LP
The functions \fBdrand48()\fR, \fBlrand48()\fR, and \fBmrand48()\fR store the
last 48-bit X(i) generated in an internal buffer. X(i) must be initialized
prior to being invoked. The functions \fBerand48()\fR, \fBnrand48()\fR, and
\fBjrand48()\fR require the calling program to provide storage for the
successive X(i) values in the array specified as an argument when the functions
are invoked. These routines do not have to be initialized; the calling program
must place the desired initial value of X(i) into the array and pass it as an
argument. By using different arguments, functions \fBerand48()\fR,
\fBnrand48()\fR, and \fBjrand48()\fR allow separate modules of a large program
to generate several \fIindependent\fR streams of pseudo-random numbers, that
is, the sequence of numbers in each stream will \fInot\fR depend upon how many
times the routines have been called to generate numbers for the other streams.
.sp
.LP
The initializer function \fBsrand48()\fR sets the high-order 32 bits of X(i) to
the 32 bits contained in its argument. The low-order 16 bits of X(i) are set to
the arbitrary value 330E(16) .
.sp
.LP
The initializer function \fBseed48()\fR sets the value of X(i) to the 48-bit
value specified in the argument array. In addition, the previous value of X(i)
is copied into a 48-bit internal buffer, used only by \fBseed48()\fR, and a
pointer to this buffer is the value returned by \fBseed48()\fR. This returned
pointer, which can just be ignored if not needed, is useful if a program is to
be restarted from a given point at some future time \(em use the pointer to get
at and store the last X(i) value, and then use this value to reinitialize using
\fBseed48()\fR when the program is restarted.
.sp
.LP
The initialization function \fBlcong48()\fR allows the user to specify the
initial X(i) the multiplier value \fIa\fR, and the addend value \fIc\fR.
Argument array elements \fIparam[0-2]\fR specify X(i), \fIparam[3-5]\fR specify
the multiplier \fIa\fR, and \fIparam\fR[6] specifies the 16-bit addend \fIc\fR.
After \fBlcong48()\fR has been called, a subsequent call to either
\fBsrand48()\fR or \fBseed48()\fR will restore the ``standard'' multiplier and
addend values, \fIa\fR and \fIc\fR, specified above.
.sp
.LP
For a more powerful random number generator, see \fBarc4random\fR(3C).
.SH ATTRIBUTES
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	Safe
.TE

.SH SEE ALSO
.BR arc4random (3C),
.BR rand (3C),
.BR attributes (7),
.BR standards (7)
